Catalytic conversion of hydrocarbons



Patented Mar. 7, 1944 CATALYTIC CONVERSION OF HYDROCARBONS Aristid V.Grosse and Jac assignors to Uni que 0. Morrell, Chicago, versal OilProducts Company, Chicago, 111., a corporation of Delaware No Drawing.Application November 29, 1939, Serial No. 306,680

9 Claims. (Cl. 260-6735) The present invention relates particularly to aprocess for the conversion of hydrocarbons such as the heavierdistillate fractions of petroleum generally in the presence of compositecatalysts to produce substantial yields of gasoline boiling rangefractions containing increased proportions of cyclic hydrocarbons. Theprocess is also applicable to conversions involving single hydrocarbons,synthetically produced hydrocarbon mixtures or primary distillatesproduced in the destructive distillation of hydrocarbonaceous materialssuch as coals, lignites and shales.

One of the prime objects of this invention is to process hydrocarbons inthe presence of mixed catalysts having active principles favoring notonly cracking or splitting reactions of the carbon to'carbon bondsbutalso favoring dehydrogenation and cyclization of hydrocarbon chainsthereby increasing the proportion of desirable aromatic hydrocarbons inthe low boiling fractions I formed. The ,catalytically controlledreactions involve primary and concurrent secondary reactions but thesecondary reactions are not for the greater part of a destructivecharacter and do not form polymers nearly as extensively as in chainedhydrocarbons present more or less in most petroleum charging stocks aswell as hydrocarbons containing aromatic or naphthenic pyrolyticcracking. The formation of branched chain and cyclic hydrocarbons isincreased by the present process and the minor proportions ofcarbonaceous residue formed on the catalysts are removable by oxidation.The yield varies depending upon the boiling point range and thehydrocarbon character of the charging stock, and the components and modeof preparation of the catalyst. The composite catalysts which areselective in promoting the desired reactions are characterized by theirease of regeneration and their refractory condition which enables themto maintain their high degree of activity over extended periods of timeunder the high temperature conditions of use and regeneration.

In one specific embodiment, the present invention comprises a processfor converting higher boiling hydrocarbon fractions, vaporizable withoutsubstantial decomposition, into low-boiling fractions containingincreased proportions of cyclic hydrocarbons which consists incontacting said higher boiling fractions at elevated temperature withcatalysts composited from refractory silica-alumina catalytic massestogether with supported oxides of the elements inthe left-hand columnsof group VI of the periodic table comprising chromium, molybdenum,tungsten and uranium. w

Y The present process depends primarily upon the fact that conversionreactions involving long nuclei with long side chains, are effectedcausing the cleavage of carbon to carbon bonds and partialdehydrogenation of carbon to hydrogen bonds with more or less formationof aromatic compounds in the low boiling product by cyclizationreactions. Cyclic saturated compounds present, such as cycloparaflins,are dehydrogenated to further increase the overall yield of aromaticcompounds thereby also increasing the desirable qualities of the productsuch as antiknock value. As a result of these reactions there is anincrease of components such as benzene, toluene, and xylene in thegasoline product and increased proportions of hydrogen in the by-productgases. Obviously, the complete attainment of these reactions is notpossible in practice nor are all compounds of the exact nature typifiedby the aromatic compounds named, but many related compounds exist in thedistillate fractionslproduced. In general, the cyclization principleeffects not only the cyclization reactions of chains resulting fromhydrocarbon decomposition but also brings about dehydrogenation ofnaphthenic rings to produce desirable aromatic components.

The components in the composite catalysts of the present inventioneffecting the splitting reaction may comprise, for example, artificiallyproduced and promoted silicates such as silicaalumina complexes ornatural silica combinations such as bento'nites and montmorillonites,either raw or acid treated, permutites and other active materials suchas certain phosphates of aluminum, zirconium, and titanium. Thesecatalytically active materials may have their refractory conditionenhanced by the inclusion of so-called supports which in themselves veryfrequently have little or no catalytic influence. Diatomaceous earth,kieselguhr, numerous other clays and earth's, crushed silica, crushedfirebrick, andstructure of-the catalyst under the prolonged thestructural proper-- mercial' practice.

One preferred method of preparing the cracking component incorporatedinto the composite catalyst of the present invention is to admixprecipitated silica gel and precipitated alumina under conditionswhereby the final catalytic material will be substantially free fromreacting materials introduced in the process of preparation.

The silica gel may be precipitated from an aqueof an acid, such ashydrochloric acid for example. The excess acid and the concentration ofthe solution in which the precipitation is finally brought aboutdetermine the suitability of the silica hydrogel for precipitatedalumina. The alumina may be precipitated in the presence of the washedor purisubsequent 'compositing with ous solution of sodium silicate bythe addition H cyclization principle are deposited upon the base oxidesshould be deposited in relatively minor amounts upon the base materialor carrier, usually in amounts of the order of less than percent byweight of the base material. The more common practice is to utilize 2-10percent by weight of these oxides and they are preferably produced insitu from precipitated hydroxides or by the partial reduction of higheroxides remaining as a residue after the ignition of adsorbed saltscontaining a. volatile acid radical. These oxides, or promotersso-called, essential in the material and include generally compounds andmore usually the oxides of the elements in the left-hand column of groupVI of the periodic table including chromium, molybdenum, tung- -sten anduranium, Many of the compounds of the preferred elements are useful inproducing Y catalytically active material but the oxides, and

fled silica'gel by suspending the silica gel in an aqueous solution ofaluminum salt and precipitating alumina by the addition of an alkalinemedium such as ammonium hydroxide. tively, the silica gel and aluminamay be coprecipitatedirom a solution of water glass to which solublecompounds of aluminum are added together with suitable precipitatingagents. In any event the silica gel and precipitated alumina are veryintimately associated in the esulting silica-alumina complex. Whateverthe form or typeof cracking principle used and whether more or lessinert supports are added or not, the cracking portion of the catalyst isvery intimately mixed with the remaining principle incorporated into thecomposite catalyst as subsequently described.

The components or principles entering into the composite catalyst of thepresent invention which are efiective in facilitating the cyclizationand dehydrogenation reactions may be of a supported character. Variousmaterials having the necessary physical and chemical characteristics forcatalysts are available. There are three hydrated oxides of aluminumoccurring in nature, hydrarglllite' and gibbsite having the formulaA1203.3H2O, bauxite having the formula and diaspora having the formulaA1203.H2O. Of these three minerals, only the oxides produced from thebauxite and gibbsite are suitable for the manufacture of the presenttype of catalyst and this material has given good results. Suitableiorms of alumina may be made by calcining tri-hydrates if they are inthe proper crystalline form, the suitability and activity of thecalcined oxide depending upon the care observed in preserving theirporous structure. Precipitated trihydroxide may likewise be employed asthe catalyst carrier when observing similar precautions. In the finalsteps of preparing aluminum oxide as a base material it is best practiceto ignite or calcine it at temperatures within the approximate range of1100-1600" F. This does not corto complete dehydration of the hydratedcatalytic material of good respond oxides but yields a strength andporosity so as to resist for a long period of time the deterioratingeffects of the higli'temperatures used in the contact and re-.

Alternain some cases with good of chromium comprises essentiallymixtures of.

major amounts of inert carriers and minor amounts of compounds ofchromium such as, for example, the oxides CrOz, C103 and particularlythe sesquioxide, CrzOa which results from the reduction of the twohigher oxides. Such compounds as chromic acid, H2C1'O4, prepared bydissolving the trioxide in water, and chromium nitrate CI(NO3)3 arereadily soluble in water at ordinary temperatures, their solutions areutilizable for adding compounds to various carriers, and on ignitingleave a residue of the trioxide which later becomes reduced to the greensesquioxide. Similarly the chromium hydroxides may be precipitated fromaqueous solutions onto the carrier in bulb or as suspended particles bythe use of alkaline precipitants such as ammonium hydroxide orcarbonate, for example. Numerous readily soluble compounds of molybdenummay be used in solution to deposit lower oxides of molybdenum such asthe sesquixode, M0203 and the dioxide, M002. Examples of readilyavailable compounds are molybdbenum pentachloride in hydrochloric acidsolution, molybdic oxide dissolved in aqueous ammonia, ammoniummolybdate, and molybdenum oxychloride. Oxides of tungsten such as thesesquioxide, W203 and the dioxide, W02 which result from reduction ofthe trioxide, W03, appear to be the active oxides of tungsten. Tungsticacids may be precipitated from aqueous solutions by the use of alkalineprecipitants and may be precipitated upon a carrier and the hydroxidesubsequently ignited to form mixtures of trioxide and dioxide which arelater probably modified in forming the active principle of the catalyst;Uranium is the heaviest and rarest member of the present naturalgrouping of elements. There are a series of oxides and these will havevery active properties when properly prepared in promoting the desiredreactions.

Generally, in the preparation of the composite catalysts of the presentinvention, the cracking components on the one hand and the cyclizationcomponents on the other hand, are sepa- Thepromoting marately preparedand may be admixed in the wet or dry condition and formed into particlesor pellets for contacting with the hydrocarbons. It appears preferableto intimately admix these materials while in the wet conditionpreliminary to drying and forming of the contact masses. Although usefulresults may be achieved using rather wide ratios of the functioningcomponents, the best results appear to be obtained when using minorproportions of the dehydrogenation and cyclization component and majorproportions of the cracking components, for example to 40 parts of theformer and 100 parts of the latter. After said components have beenintimately mixed, as for example by slurrying a freshly preparedprecipitated silica-alumina in admixture with the wet materialconsisting of molybdenum oxide disposed on an alumina support, thispreparation may be freed from excess water and extruded directly ordried and formed into shaped particles. Frequently it is more economicpractice to wash the aggregate after it had been dried, with suitablewashes, since the impurities may be intimately associated with the gelor particle structure and therefore very difiicult to remove by washingtreatments. Subsequently the material is heated at high temperatures,more usually after the catalytic masses are formed into particles,whereby the catalyst assumes the active form necessary for prolonged usein the desired hydrocarbon reactions. This temperature is of the'orderof 1000-l500 F., more or less, a temperature such as 1400 F. for examplebeing desirable.- Despite these high temperatures of heating, smallproportions of water of the order of 2-5% appear to be associated withthe catalytic material.

Catalysts prepared in general accordance with the procedures aboveoutlined apparently possess a large total contact surface correspondingto a desirable porosity, the pores of the catalyst particles being ofsuitable size and shape so as not to become permanently clogged withcarbonaceous deposits when in continued service. The catalysts aretherefore not diificult to reactivate by oxidation and they retain theirhigh degree of activity after the high temperature conditions ofalternate use and reactivation for long periods of time.

In common with many other catalytic processes, the composite catalyst ofthis invention may be conveniently utilized in carrying out the desiredreactions when employed as filling material in tubes or chambers in theform of small pellets or granules. The average particle size may varywithin the approximate range of 2 or 3 to 10 mesh which may apply toeither pellets of uniform ,size, short cylindrical shapes, or toparticlesof irregular size and shape produced by consolidating andsizing the powdered catalytic material. While the simple method ofpreheating a, given fraction of hydrocarbon oil to be processed at atemperature suitable for conversion in contact with the catalyst andthen passing the vapors over a stationary mass of the catalyst particlesmay be employed in some cases, it is generally more preferable to passthe preheated vapors through beds of catalyst where the. passage ofvapors is restricted to definite paths rather than .unrestricted contactto large beds of catalytic material. It is thus possible to moreaccurately control the temperature of the catalyst in use and duringregeneration by various heat inter-- change devices and mediums. Afterthe passage with the charging stdck or processed in separate passes soas to ultimately obtain the maximum utilization of the charging stock inproducing the desired gasoline product. Although the above consists inthe more conventional practice, it is also possible to-suspend thecomposite catalyst in a stream of oil as a powder and treat thesuspension under suitable conditions of pressure, and contact time. Thegaseous olefins appearing in the product and the hydrogen aresusceptible to the conventional processes of polymerization and hydrogenconcentration.

The application of the present invention to the processing ofhydrocarbon fractions besides being characterized by the use of novelcatalysts is also of importance because of the moderate operatingconditions of temperature and pressure. Temperatures employed in contactwith the catalysts may be within the range-of 750-1250 F.,

" more or less, and substantially atmospheric'pressure or moderatelysuperatmospheric pressures such as those up to a few hundred pounds persquare inch may be used. Usually pressures below 100 pounds per squareinch are used, the pressures being in some measure conditions throughthe vaporizing and conversion zones and the subsequent separating,fractionating, and collecting equipment.

The following specific example is given to illustrate the process of theinvention, a method of catalyst preparation also being given. The process should not be considered as limited to this example or to the itbeing given merely as illustrative of the novelty and utility of theinvention.

Catalyst prepared according to the present invention consistedapproximately of one part of cyclization component and 4 /2 parts'of thecracking principle. The general procedure observed in preparing thiscatalyst was to precipitate a silicaalumina composite, add a.cyclization catalyst in finely divided form to an aqueous suspension ofthe silica-alumina composite to form an intimate admixture.

A commercial grade of sodium silicate was diluted approximately 10 timesand dilute hydrochloric acid solution gradually added while agitatinguntil the solution was very slightly acid whereupon av hydrated silicagel was formed. This gel was washed and then slurried in a diluteaqueous solution of aluminum chloride of the desired concentration.Aluminum hydroxide was then precipitated in the presence of thesuspended silica by the addition of ammonium hydroxide. The amount ofsilica gel and aluminum salt reacted was such as to give a composite ofthe following approximate composition:

100SlO225A12O3 The cyclization part was prepared by precipitatingmolybdic hydroxide upon activated alumina granules from a solution ofthe desired strength intermediate insufiiciently temperature,

also governed by flowparticular catalyst preparation,

respectively. The composite was dried at approximately 250 F. and thedried powdered material was washed to remove soluble impin'ities andthepurified material was then again dried. The dried material was mixedwith a small amount of lubricant and pilled to form pellets ofapproximately inch size and the pelleted catalyst was calcined at atemperature of approximately 1200 F. for several hours.

Catalyst particles from the above preparation were disposed in avertical cylindrical chamber and vapors of a Pennsylvania gas oilpreheated to "a temperature of 880 F. were directed downwardly throughthe catalytic materials using an hourly liquid space velocity ofapproximately 0.8.

The gas formed during the reaction was separated from the liquidproducts and the gasoline recovered from the partially converted gas oilby distillation. In a single pass, 28 volume percent of the chargingstock was converted to 80 octane number gasoline. This gasoline had ahigher aromatic hydrocarbon content than gasoline produced from the samecharging stock in the presence of silica-alumina catalyst alone. Runsmade using quartz chips in place of the catalyst when processing gasoilunder similar conditions gave a yield of only 4% having considerablylower octane number.

We claim as our invention:

A process for producing low boiling aromatic hydrocarbons fromhydrocarbon oils heavier than gasoline and containing aliphatics,'whichcomprises subjecting the oil to a non-hydrogenating cracking anddehydrocyclization treatment in the presence of an oxide of an elementfrom the lefthand column of group VI of the periodic table admixed witha cracking catalyst comprising a major proportion of silica and a minorproportion of alumina.

2. A process as set forth in claim 1 where the oxide of the element fromthe left-hand column of group VI of the periodic table is supported upona relatively inert refractory material.

3. A process as set forth in claim 1 where the oxide of the element fromthe left-hand column of group VI of the periodic table is supported upona calcined aluminum hydrate.

4. A process as set forth in claim 1 where the cracking catalyst is anacid treated clay.

5. A process as set forth in claim 1 where the cracking catalystcomprises a purified precipitated silica gel.

6. A process as set forth in claim 1 where the crackingcatalyst ischaracterized by having been prepared from precipitated silica gel andprecipitated hydrous alumina.

'7. A process for converting high boiling hydrocarbons into substantialyields of gasoline of high antiknock value which comprises subjectingsaid hydrocarbons to a non-hydrogenatin'g cracking and'dehydrocyclization treatment at a temperature within the approximaterange of 750-1250 F. and in the presence of a precipitated and washedsilica gel which has been impregnated with precipitated alumina, saidimpregnated material having been further admixed with a supported oxideof an element selected from the left-hand column of group VI of theperiodic table.

8. A process for converting high boiling hydrocarbons into substantialyields of gasoline of high antiknock value which comprises subjectingsaid hydrocarbons to a non-hydrogenating cracking and dehydrocyclizationtreatment at a temperature within the approximate range of 750-1250 F.and in the presence of a precipitated and washed silica gel which hasbeen impregnated with precipitated alumina, said impregnated materialhaving been further admixed with a supported oxide of an elementselected from the left-hand column of group VI' of the periodic table,fractionating and separating the conversion products to producegasoline, hydrocarbon oil above the motor fuel boiling point range, anda normally gaseous fraction comprising relatively high percentage ofreadily polymerizable olefins and hydrogen.

9. A process for converting high boiling hydrocarbons into substantialyields of gasoline of high antiknock value which comprises subjectingsaid hydrocarbons to a non-hydrogenating cracking andclehydrocyclization treatment at a temperature within the approximaterange of 750-1250 F. and in the presence of a precipitated and washedsilica gel which has been impregnated with precipitated alumina, saidimpregnated material having been further admixed with a supported oxideof an element selected from the left-hand column of group VI of theperiodic table, fractionating and separating conversion products toproduce gasoline liquid recycle stock and a normally gaseous fractioncomprising relatively high percentages of readily polymerizable olefinsand hydrogen, and returning said liquid recycle stock'to contactwithsaid catalytic material for further treatment.

ARISTID V. GROSSE. JACQUE C. MORRELL.

